The ROS1 gene encodes receptor tyrosine kinase discovered as a human ortholog of the cancer gene product v-ros of avian sarcoma virus UR2 (University of Rochester tumor virus 2) (Non Patent Reference 1). The ROS1 fusion gene resulting from the chromosomal rearrangement containing the ROS1 gene and the subsequent fusion of the ROS1 gene to another gene was discovered in a lioblastoma cell line U118MG. In the U118MG cells, a gene encoding a Golgi protein FIG (fused in glioblastoma) is fused with the ROS1 gene to form a gene encoding FIG-ROS1 fusion protein (Non Patent Reference 2). The fusion between FIG and ROS1 causes structural change that constitutively activates ROS1 kinase enzyme activity, and the FIG-ROS1 fusion protein has cell transformation activity and tumorigenic activity mediated by the activation of the ROS1 signaling pathway involving STAT3, ERK, and SHP2 (Non Patent References 3 and 4).
The chromosomal translocation of the ROS1 gene has also been identified in a non-small cell lung cancer cell line HCC78 and clinical specimens of lung cancers. The fusion gene of the SLC34A2 gene and the ROS1 gene has been reported in the HCC78 cells, while the presence of the transmembrane protein-encoding CD74-ROS1 fusion gene of the CD74 gene and the ROS1 gene has been reported in non-small cell lung cancer patient specimens (Non Patent Reference 5). The fusion gene of the FIG gene and the ROS1 gene has been found in 2 out of 23 patient specimens of bile duct cancer (Non Patent Reference 6).
The large-scale screening of patient specimens using FISH (fluorescent in situ hybridization) has identified fusion genes of the ROS1 gene with SDC, CD74, EZR, SLC34A2, LRIG3, or TPM3. Any of the ROS1 fusion genes SDC-ROS1, CD74-ROS1, EZR-ROS1, SLC34A2-ROS1, LRIG3-ROS1, and TPM3-ROS1 have been detected in 13 out of 1476 non small cell lung cancer patient specimens (Non Patent Reference 7).
Likewise, the large-scale screening of non-small cell lung cancer patient specimens using FISH has found the ROS1 fusion gene in 18 out of 1073 cases (Non Patent Reference 8). In addition, analysis using patient specimens has showed that the ROS1 gene is highly expressed in brain tumor (Non Patent References 1 and 9).
ROS1 has been shown to be activated in cancer expressing the ROS1 fusion gene (e.g., non-small cell lung cancer, bile duct cancer, or brain tumor) (Non Patent References 5 and 6). Thus, a drug that inhibits ROS1 kinase activity can block the downstream of the ROS1 pathway, i.e. STAT3, ERK, SHP2, which contribute the tumor growth and tumor cell survival. Therefore, ROS1 is expected to be useful as a therapeutic drug for cancer (Non Patent References 1, 6, and 8). Compounds such as crizotinib (Non Patent Reference 8), TAE684 (Non Patent Reference 6), pyrazole derivatives (Non Patent References 10 and 11), and aminopyrazine derivatives (Patent Reference 1) have been reported to have a ROS1 kinase enzyme activity inhibitory effect. These compounds, however, differ in structure from the compounds of the present invention.
Neurotrophic tyrosine kinase receptor, also called tropomyosin-related kinase (Trk), is a high-affinity receptor that is activated by a soluble growth factor called neurotrophin (NT). The NTRK receptor family has three members: NTRK1 (also called TrkA), NTRK2 (also called TrkB), and NTRK3 (also called TrkC).
NT includes a plurality of proteins as follows: a nerve growth factor (NGF) which activates NTRK1, a brain-derived neurotrophic factor (BDNF) and NT-4/5 which activate NTRK2, and NT3 which activates NTRK3. Each NTRK receptor contains an extracellular domain (ligand-binding site), a transmembrane domain, and an intracellular domain (containing a kinase domain). Upon binding to a ligand, each kinase catalyzes autophosphorylation and then activates the downstream signal transduction pathway.
NTRK is widely expressed in nerve tissues during their development period and plays an important role for the maintenance and survival of these cells. The previous study shows that NTRK plays an important role in both the development and function of the nervous system (Non Patent Reference 12).
A large number of references state that NTRK signal transduction is associated with cancer. For example, NTRK exists at a low expression level in regions other than the nervous system in adult humans, whereas the expression of NTRK is increased at the late stage of prostate cancer. In normal prostate tissues and androgen-dependent prostate tumor at the early state, NTRK1 is expressed only at a low level or an undetectable level, but neither NTRK2 nor NTRK3 is expressed. In androgen-independent prostate cancer at the late stage, however, all isoforms of the NTRK receptors and their ligands are overexpressed. The evidence shows that these late-stage prostate cancer cells depend on NTRK for their tumor survival. Thus, NTRK inhibitors may induce apoptosis for androgen-independent prostate cancer (Non Patent Reference 13). In addition, recent references also show that the overexpression, activation, amplification, fusion gene formation, or mutation of NTRK is related to neuroblastoma (Non Patent Reference 14), secretory breast cancer (Non Patent Reference 15), colorectal cancer (Non Patent Reference 16), ovary cancer (Non Patent Reference 17), head and neck cancer (Non Patent Reference 18), pancreatic cancer (Non Patent Reference 19), and melanoma (Non Patent Reference 20).
Selective NTRK tyrosine kinase inhibitors have been reported, including CEP-751, CEP-701 (Non Patent Reference 21), indolocarbazole compounds (Patent Reference 2), oxindole compounds (Patent References 3 and 4), pyrazolyl condensed-ring compounds (Patent Reference 5), isothiazole compounds (Non Patent Reference 22), and other various compounds (Patent References 6, 7, 8, 9, and 10). These compounds, however, differ in structure from the compound of the present invention.
Lck inhibitors (Patent Reference 11), PKC inhibitors (Patent References 12 and 13), and NTRK inhibitors (Patent References 14 and 15) are known as compounds having an imidazopyridazine skeleton. Nevertheless, none of the known compounds having an imidazopyridazine skeleton exhibit ROS1 kinase enzyme inhibitory activity and NTRK inhibitory activity.